This invention relates generally to the field of surface plasmon resonance sensors and, more particularly, to the field of sensors used in the fields of chemical, biochemical, biological or biomedical analysis, process control, pollution detection and control, and other similar areas.
Surface plasmon resonance is an optical surface phenomenon that has been employed in sensors used in the fields of chemical, biochemical, biological or biomedical analysis. A surface plasmon is a surface charge density wave at the surface of a thin conducting film. This resonance can be observed when a polarized beam of monochromatic electromagnetic radiation is totally internally reflected from a dielectric interface having a thin metal film formed thereon. Usually the interface comprises a smooth surface of a transparent body such as glass. The electromagnetic radiation internally reflected by the interface has a minimum intensity at a particular angle referred to as resonant angle. This angle is determined by the dielectric conditions adjacent the metal film and the properties of the film itself.
The basis for the use of surface plasmon resonance for sensing is the fact that the oscillation of a surface-plasma of free electrons which exists at a conductor-dielectric boundary is affected by the refractive index of the material adjacent the conducting film surface on the side thereof opposite the reflected polarized electromagnetic radiation. For a given wavelength of radiation, the resonance occurs when the angle of incidence of the polarized radiation has a particular value and this value, dependent on the refractive index, gives rise to changes in the angle at which surface plasmon resonance occurs. When polarized electromagnetic radiation strikes the thin metal film at the resonance angle, the intensity of the reflected electromagnetic radiation therefrom is minimized. A reflecting surface reflects the electromagnetic radiation reflected from the surface upon which the surface plasmon resonance occurs towards a one dimensional array of detectors. Hence, by detecting the angle at which the minimum intensity of electromagnetic radiation occurs, the refractive index of the material adjacent the film can be determined. The usefulness of this approach, however, has been limited due to the criticality of the reflecting surface. In addition, the number of materials capable of being detected directly corresponding to the number of channels is limited.
Therefore, it would be desirable to have a surface plasmon resonance sensor having a multiplicity of channels without the need for a reflecting surface.
The problems associated with earlier sensors are overcome by the present invention which provides a surface plasmon resonance sensor capable of determining the property of several liquids at varying times or simultaneously without the need for a reflecting surface. The sensor includes an electromagnetic radiation source which generates a beam of electromagnetic radiation that passes through a filter and a polarizer disposed between the source and an array of detectors. The filter prevents electromagnetic radiation at the absorbed frequency from striking the array. A film of a conductive material capable of sustaining surface plasmon resonance has a first surface and a second surface. Liquids are deposited on the first surface, while the second surface reflects at least part of the beam of electromagnetic radiation generated by the source. The array of electromagnetic radiation detectors detect part of the beam of electromagnetic radiation to make a determination of a property of the plurality of liquids and produce an output signal in response to the received portion of the reflected electromagnetic radiation indicative of the presence of, or representative of the concentration or a concentration range of, the liquid. This array may be one, two, or three dimensional.
Furthermore, the surface plasmon resonance sensor may include a number electromagnetic radiation sources to increase the number of channel capacity. Another embodiment may provide controller coupled to the number of electromagnetic radiation sources for switching each source on and off so that all sources are turned on simultaneously or in a sequential order.